1. Field of the Invention
The present invention relates to computing systems, and more particularly to arbitration techniques requesting bus/memory access.
2. Background of the Invention
Conventional computing systems typically include several functional components. These components may include a central processing unit (CPU), main memory, input/output (“I/O”) devices, and streaming storage devices (for example, tape drives). In conventional systems, the main memory is coupled to the CPU via a system bus or a local memory bus. The main memory is used to provide the CPU access to data and/or program information that is stored in main memory at execution time. Typically, the main memory is composed of random access memory (RAM) circuits. A computer system with the CPU and main memory is often referred to as a host system.
Host systems are used in various network applications, including storage area networks (“SANs”). In SANs, plural memory storage devices are made available to various host computing systems. Data in a SAN is typically moved between plural host systems and storage systems (or storage devices, used interchangeably throughout this specification) through various controllers/adapters. Host systems often communicate with storage systems via a host bus adapter (“HBA”, may also be referred to as a “controller” and/or “adapter”).
Host systems often communicate with peripheral devices via an interface such as the Peripheral Component Interconnect (“PCI”) interface, a local bus standard that uses parallel data transfer, or the extension of PCI known as PCI-X. Both the PCI and PCI-X standard specifications are incorporated herein by reference in their entirety.
More recently, PCI-Express, a standard interface incorporating PCI transaction protocols has been developed. PCI-Express is an Input/Output (“I/O”) bus standard (incorporated herein by reference in its entirety) that is compatible with existing PCI cards using the PCI Express bus.
HBAs (a PCI-Express device) that are placed in SANs, receive serial data streams (bit stream), align the serial data and then convert it into parallel data for processing. HBAs operate as a transmitting device as well as a receiving device.
Arbitration modules are used in HBAs and other devices (mainly in application specific integrated circuits (ASICs)) to allow access to a bus or a memory location. An arbitration module typically receives requests from different components, for example, direct memory access (“DMA”) modules. The arbitration module then arbitrates between the requests and grants access to the winning request. Typically, a round-robin scheme is used to determine which request wins arbitration.
ASIC performance expectations are increasing with high-speed designs. Traditional arbitration techniques are not able to meet the high-speed demand and expectations.
Therefore, there is a need for a method and system for improving arbitration techniques.